(1) Field of the Invention
The present invention relates to the field of apparatus for introducing air into a hydropneumatic reservoir or network provided in hydraulic pipework, notably in a network for discharging waste water or chemical liquids.
(2) Description of Related Art
A hydropneumatic reservoir may be used as an anti-pressure surge reservoir of a hydraulic pipework or network in order to compensate the effects of underpressure and overpressure produced for example by stoppage of a pump or the closure of a valve. The operation of such a reservoir is known in particular from the document FR 2416417. In such a reservoir, the pressurised water or liquid located at the lower end is surmounted by air or gas, which is also pressurised, the quantity of which has to remain substantially constant to ensure correct operation of the apparatus. In fact, if there is a lack of air, the pipework is inadequately protected, and if there is too much air there is a risk of air escaping into the pipework, which must be prevented.
The publication EP 0617227 describes a system for regulating air for a hydropneumatic reservoir comprising an air introduction chamber which can be evacuated by means of an evacuating solenoid valve. A solenoid valve for taking air into the chamber is opened. Then the two first solenoid valves are closed and a solenoid filling valve is opened in order to drive air towards the reservoir. The solenoid valves are controlled by control means connected to a detector which emits a signal in the event that the water level becomes higher than the level of the detector. This system requires an electricity supply, which may prove expensive in zones remote from the electricity grid, and causes the escape of a certain amount of liquid, which is not really desirable in the case of drinking water and should obviously be prevented in the case of other liquids.
In the field of pumping water, even contaminated waste water, the dissolution of air in the water is greater than the release of gases. It is therefore important to compensate an air deficit.
The publication EP 0895020 describes an air introduction apparatus for a hydropneumatic reservoir in which the air is introduced into a low pressure zone, such as the zone upstream of a pump, by opening a solenoid valve. The losses of liquid are prevented but an electricity supply is needed and the introduction of air is controlled by means of liquid level sensors in contact with the liquid, so that operation may be disrupted by deposits when contaminated water is being pumped.
The present invention sets out to overcome these disadvantages.